已知cos(a+b)cos(a-b)=1/4,则cos^2a+cos^2b=
已知4sin asin b=根号2,4cos a cos b=根号6,则cos 2a+cos 2b的值是?
Cos(a+b)*cos(a-b)=1/5 求cos ^2-sin^2
若sin^4a/sin^2b+cos^4a/cos^2b=1,证明sin^4b/sin^2a+cos^4b/cos^2a
已知cos(a+b)cos(a-b)=1/3 ,求(cosa)^2-(cosb)^2
求证:a^2(cos^2b-cos^2c)+b^2(cos^c-cos^2a)+c^2(cos^2a-cos^2b)=0
cos(a+B)×cos(a-B)=1/3,求cos^2(a)-sin^2(B)的值
cos(A+B)cos(A-B)=1/4 求cosA^2+cosB^2
已知cos(a-b)=-12/13 cos(a+b)=12/13且π/2
1]已知tana*tanb=2,(*是×)则cos(a+b)*cos(a-b)/(cosa)^2*(cosb)^2=
由cos(a+b)=cos a cos b-sin a sin b cos(a-b)=cos a cos b+sin a
已知向量a=(cosα,sinα),b=(cosβ,sinβ),|a-2b|=|√2a+b|,则cos(α-β)=___
已知A,B为锐角,cosA=4/5,tan(A-B)=-1,求cos((A+B)/2)*cos((A-B)/2)的值